Method for manufacturing a tetrafluoroethylene polymer-coated roll

ABSTRACT

Tetrafluoroethylene resin-coated fuser rolls, in which the resin is applied in a single-fusion process, for use in xerographic reproducing apparatus. The single-fusion process involves successive application of tetrafluoroethylene coats 0.6 to 0.9 mil thick until a coating of about 6 mils is attained. Between each application, the rolls are heated to about 180* F. in order to flash off water and volatile materials. The coating is fused by a single baking step at the end of the process.

\ tes atent [1 1 er et a1.

[ METHOD FOR MANUFACTURING A TETRAFLUOROETHYLENE POLYMER-COATED ROLL [75] Inventors: John R. Baker, Webster; Edward G.

Williams, Macedon, both of NY.

[52] 11.8. C1 117/72, 29/1295, 117/75, 117/94,117/119.6,117/132 CF, 117/161 UF, 118/101 [51] Int. Cl B4411 1/14, B30b 3/00 [58] Field of Search 117/72, 94, 161 UP, 117/132 CF, 119.6, 75

[56] References Cited UNITED STATES PATENTS 3,437,032 4/1969 Manghirmalani et a1 117/75 X 2,979,418 4/1961 Dipner 117/161 UF X 3,554,955 1/1971 Hartwimmer et 117/132 CF X 3,341,348 9/1967 Letendre 117/132 CF X 3,514,314 5/1970 3,644,260 2/1972 Strolle 117/72 X Primary Examiner-Ra1ph Husack Attorney-James J. Ralabate et al.

[57 ABSTRACT Tetrafluoroethylene resin-coated fuser rolls, in which the resin is applied in a single-fusion process, for use in xerographic reproducing apparatus. The singlefusion process involves successive application of tetrafluoroethylene coats 0.6 to 0.9 mil thick until a coating of about 6 mils is attained. Between each application, the rolls are heated to about 180 F. in order to flash off water and volatile materials. The coating is fused by a single baking step at the end of the process.

3 Claims, No Drawings METHOD FOR MANUFACTURING A TETRAFLUOROETHYLENE POLYMER-COATED ROLL SURFACES WITH FLUOROCARBON PROCESS FOR MULTIPLE COATING RESINS This invention relates to improvements in heat fusing devices and, particularly, to an improved apparatus for fixing xerographic powder images.

More specifically, the invention relates to an improved heated-roll fusing device. Although the invention is considered to have general application, it is particularly useful in the field of xerography and has an important application in the fusing of resinous powder images produced by electrophotography or xerography onto sheets of paper and the like to which the powder images have been transferred after they have been formed by deposition of powder on an electrostatic latent image. Therefore, for convenience of illustration, theinvention is described with reference to its use as a heat fuser for xerographic powder images. However, it is to be understood that it may be employed with equal facility in other fields.

In the process of xerography, for example, as disclosed in Carlson U.S. Pat. No. 2,297,691, issued Oct. 6, 1942, a xerographic plate, comprising a layer of photoconductive insulating material on a conductive backing, is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas inaccordance with the radiation intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is effected with an electrostatically charged, finely divided developing material or toner which is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed xerographic powder image is usually transferred to a support surface, such as paper, to which it may be fixed by any suitable means.

One of the methods in common use for developing the electrostatic latent image is described in Walkup U.S. Pat; No. 2,618,551, and is known as cascade development, and is in general use for line copy development. In this technique, the powder or toner is mixed with a granular carrier material, and this twocomponent developer is poured or cascaded over the plate surface. The function of. the carrier material is to improve the How characteristics of the powder and to produce, on the powder, by triboelectrification, the proper electrical charge so that the powder will be attracted to the image. More exactly, the function of the carrier material is to provide the mechanical control to the powder, or to carry the powder to an image surface and, simultaneously, to provide homogeneity of polarity.

In the Carlson patent it is noted that a variety of types of finely-divided electroscopic powders may be employed for developing electrostatic latent images. However, as the art of xerography has progressed, it has been found preferable to develop line copy images with a powder or toner formed of any of a variety of pigmented thermoplastic resins that have been specifically developed for the purpose. A number of such developing materials are available commercially, and these developing materials are specifically compounded for producing dense images of high resolution and to have characteristics to permit convenient storage and handling. Such developing materials are compounded to permit them to be fixed to the surface of a transfer material either by heat fixing or vapor fixing techniques, in accordance with the particular application in which they are employed, that is, the individual particles of resin (toner) soften and coalesce when heated or plasticized by solvent, so that they become sticky or tackified and readily adhere to the surface of the transfer material.

The term tackified and the several variant forms thereof used throughout this specification are employed to define the condition of the powder particles of the xerographic powder image when heated or plasticized by a solvent in a manner such that the individual particles soften and coalesce and in which state they become sticky and readily adhere to other surfaces. Although this condition necessarily requires a flowing together of the particles to effect a thorough fusion thereof, it is to be understood that the extent of such 1 flowing is not sufficient to extend beyond the boundary phy comprises its use in automatic copying machines for general office use wherein the powder images formed on a xerographic plate are transferred to paper and then fixed thereon by heat fusing. In order to fuse resinous images formed of the powdered resins now commonly used, it is necessary to heat the powder and the paper to which it is to be fused to a relatively high temperature, such as approximately 325 F. It is undesirable, however, to raise the temperature of the paper substantially higher than 375 F. because of the tendency of paper to discolor at such elevated temperatures.

It has long been recognized that one of the fastest and mostpositive methods of applying heat for fusing the powder image to paper is to bring the powder image into direct contact with a hot surface, such as a heated flat plate.

But, as the powder image is tackified by heat, part of the image carried by the support material will stick to the surface of the heated plate, so that as the next sheet is placed on the heated plate the tackified image partially removed from the first sheet will partly transfer to the next sheet and at the same time part of the tackified image from said next sheet would adhere to the heated plate. This process is commonly referred to in printing art, as set of or offset, the latter term being preferred.

The offset of toner onto the heating surface led to the development of improved methods and apparatus for fusing the toner image, notably the process and apparatus described in Van Dorn U.S. Pat. No. 3,268,351, issued Aug. 23, 19.66. The toner images were fused by forwarding the sheet or web of paper bearing said image between two heated rolls, the roll contacting the image being provided with a thin coating of tetrafluoroethylene resin and a silicone oil film to prevent toner offset. The tetrafluoroethylene resin is sold under the trademark Teflon by E. l. DuPont De Nemours & Co. Both the tetrafluoroethylene resin and the silicone oil have physical characteristics such that they are substantially abhesive to dry or tackified xerographic developing materials. Abhesive is a relatively new term coined by the Dow Corning Corporation, primarily in connection with their silicone to define a surface that has release characteristics such that it is highly repellent to sticky or tacky substances.

Although the use of a tetrafluoroethylene resincoated roll in xerographic reproducing apparatus has been a great improvement, certain problems with respect to the resin-coated roll itself have developed. For example, in the ordinary process for manufacturing the resin-coated rolls, it is necessary, in order to attain sufficient resin thickness on the surface of the roll, to apply multiple coatings of resin. This has often resulted in resin coatings which are not homogeneous in thickness and which on occasion have been subject to blistering. Therefore, the durability of certain resin-coated rolls has been somewhat less than one would desire.

Furthermore, the method of manufacturing the resincoated roll heretofore used in a lengthy process involving successive baking of the coated rolls at high temperatures.

It is therefore the principal object of this invention to improve the construction of fluorocarbon, e.g., tetrafluoroethylene resin-coated rolls to provide a homogeneous thickness of resin thereon and avoid blistering.

Another object of this invention is to provide a tetrafluoroethylene resin-coated roll which will have greater durability.

Still another object of this invention is to provide the method of manufacturing the resin-coated rolls so as to achieve improved efficiency and economy.

These and other objects of this invention are attained by the means of successively applying to the roll thin coatings of tetrafluoroethylene enamel film and, between each application, heating the film-coated roll to a temperature not exceeding 180 F. so as to flash off most of the water and solvent contained in the film. When the desired thickness of coating is attained, the coated rolls are subjected to a temperature of from about 700 to 900 F., preferably 730750 F., in order to fuse the tetrafluoroethylene resin coating. This is in contrast to the previously employed method by which the rolls were heated to fusion temperature after each thin layer of tetrafluoroethylene enamel was applied.

There is thus provided a single fuse process for applying tetrafluoroethylene resin coatings to xerographic apparatus fusing devices. The resulting coating is a homogeneous layer which will not blister. Another advantage derived from the practice of this invention is that the tetrafluoroethylene primer, which must be applied to the roll before application of the tetrafluoroethylene enamel, can be cured at a temperature significantly lower than has heretofore been required.

The process of this invention is a multiple step process involving: (1) application ofa tetrafluoroethylene primer; (2) heating the primer-coated roll at a temperature sufflciently high to cause baking of the primer substance; (3) applying a thin coating of tetrafluoroethylene enamel liquid; (4) passing the enamel-coated roll through a temperature zone no higher than 180 F. in order to flash off water and solvent, repetition of steps (3) and (4) until one attains the desired thickness of tetrafluoroethylene enamel on the roll, and (5) heating the coated roll to a high temperature in order to fuse the coating.

Prior to applying the tetrafluoroethylene primer, it is essential that the surface of the roll be properly prepared. The surface should be clean and free of all greasy substances. Furthermore, adhesion of the primer is improved if the surface has been slightly roughened in a uniform manner. Methods of properly preparing the surfaces, such as solvent cleaning, grit blasting, chemical etching, wheel sanding, etc. are well known to a person skilled in the art.

After the surface of the roll has been properly prepared, the tetrafluoroethylene primer is applied. A number of primer substances are available; DuPonts Teflon 850-204 is especially suitable for application in xerographic reproducing machine fuser rolls. One coat of primer is applied and its thickness should be about 0.3 mil and no higher than 0.7 mi]. The primer film, which is a liquid, may be conveniently applied by air atomization, either manually or, preferably, automatically.

The liquid primer film typically contains 30 to 50 percent water and other volatile materials. A drying step is necessary prior to curing the film. This must be done at a temperature of 180 F. or below, and is preferably done by air drying. The drying step can also be performed at room temperature, by allowing the coated rolls to stand for 10 to 15 minutes under a low humidity conditions. After the drying step has been completed, the rolls are ordinarily subjected to a baking temperature of from about 725 to 800 F. in order to fuse the tetrafluoroethylene primer. It is essential to use these high temperatures when one uses a multifusing process in the application of the tetrafluoroethylene enamel. However, in the process of this invention, one employs only a single-fusion step in the application of the tetrafluoroethylene enamel. Under the circumstances, the baking of the tetrafluoroethylene primer can be accomplished at a significantly lower temperature, namely at about 400 F. for 20 minutes or at from 450 to 500 F. for a period of 10 minutes. The use of these significantly lower temperatures is one of the principal advantages derived from this invention. In addition to the obvious advantage of cost savings resulting from operation at lower temperatures, there is no danger of over baking the primer coat and running the risk of poor intercoat adhesion after the enamel is applied.

The application of the tetrafluoroethylene enamel coats is performed in a manner analogous to the primer coat. For purposes of this invention, one must use one of DuPonts high build tetrafluoroethylene enamels. These are substances which can be applied in thicknesses up to about 2.5 to 3.0 mils without running the risk ofmud cracking." Mud cracking is the phenomenon which occurs when a wet enamel film is too thick and the particles are pulled apart on drying because of shrinkage. Particularly suitable for application in xerographic reproducing machine rolls is Teflon l224. In the practice of this invention, each coat should have a dry film thickness of from about 0.6 to about 0.9 mil.

After the application of each tetrafluoroethylene enamel coat, a roll is subjected to a temperature no higher than 180 F., preferably from to F., in order to flash off the major portion of the water and other volatile materials contained in the film. This is conveniently done by passing the coated roll into a drying zone having the requisite temperature. After the drying is completed, the coated roll should be allowed to return to close to room temperature before application of the next enamel coating. With a drying temperature of 180 F., about 7 to 10 minutes will elapse between successive coatings.

In the process heretofore practiced, after each coating and drying step, the tetrafluoroethylene enamelcoated rolls were placed in an oven and heated at high temperature (725 to 800 F.) in order to fuse the enamel coating. Using the methods of this invention, these repeated baking steps are not necessary.

It has been found that the optimum thickness of tetrafluoroethylene resin coating on rollers used in xerographic reproducing apparatus is between about 1.5 to 6 mils. When this thickness has been achieved by successive coatings and drying, the coated roll is then subjected to a fusion temperature of from about 700 to 900 F., preferably from about 730 to 750 F. The fusion time is about 10 to 20 minutes.

The following specific example describes the method and apparatus of this invention. It is intended for illustrative purposes only and should not be construed as a limitation.

Fuser rolls for xerographic reproducing apparatus which have been coated with Teflon 850-204 primer and baked at a temperature of 475 F. are mounted on a moving conveyor. They are then carried through a spray booth past a spray gun apparatus from which they receive one coat of Teflon 851-224 enamel, with a dry film thickness of 0.9 mil. After about 1 /2 minutes, the rolls pass through a flash-off zone where they are subjected to warm dry air at the temperature of 180 F. The volatile solvents and approximately 70 percent of the water in the enamel film are removed by this treatment. The conveyor speed is adjusted so that the parts sprayed with the Teflon 851-224 enamel are again presented to the spray guns in about 10 minutes. The cycle of spraying and drying is continued for four more passes until a film of about 5.4 mils is attained. The rolls are then removed, placed in baskets and air dried in a baking oven at a temperature of about 170 F. After this final drying process is completed, the coated rolls are removed immediately to a fusing oven where the temperature is maintained at about 720 F. The rolls are subjected to this temperature for minutes. They are observed to have a durable non-laminar coatmg.

While the present invention as to its objects and advantages, have described herein, has been carried out in specific embodiments thereof, it is not desired to be limited thereby, but is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

l. A method for manufacturing a tetrafluoroethylene polymer-coated roll for use in a xerographic reproducing apparatus for fixing a resin-based powder image onto a support surface to which the powder is loosely adhering, said method comprising the steps of:

applying to the surface of the roll a tetrafluoroethylene primer;

heating the primer-coated roll until the primer is baked;

applying to the surface of said roll a liquid coating of essentially tetrafluoroethylene enamel in a thickness of from about 0.6 to about 0.9 mil; heating the roll to a temperature not exceeding 180 F. in order to flash off water and solvent; applying additional liquid coatings of tetrafluoroethylene enamel in a thickness of from about 0.6

to about 0.9 mil and heating the roll after each application to a temperature not exceeding 180 F., until the desired thickness of tetrafluoroethylene enamel on the surface of the roll is attained; and,

heating the coated roll at a temperature of from about 725 to 800 F. until fusion of the tetrafluoroethylene coating is complete. 2. A method for manufacturing a tetrafluoroethylene polymer coated roll for use in a xerographic reproducing apparatus for fixing a resin-based powder image onto a support surface to which the powder is loosely adhering, said method comprising the steps of:

applying to the surface of the roll a tetrafluoroethylene primer in a thickness of from about 0.3 to about 0.7 mil;

heating the primer-coated roll at a temperature of from about 450 to 500 F. until the primer is baked; applying to the surface of said roll a liquid coating of essentially tetrafluoroethylene enamel in a thickness of from about 0.6 to about 0.9 mil;

heating the roll to a temperature of from about to 180 F. in order to flash off water and solvent;

applying additional liquid coating of tetrafluoroethylene enamel in a thickness of from about 0.6 to about 0.9 mil and heating the roll after each application to a temperature of between about 150 to about 180 F., until up to about a 6 mil thickness of tetrafluoroethylene enamel is attained on the surface of the roll; and,

heating the coated roll to a temperature of from about 730 to 750 F. until fusion of the tetrafluoroethylene coating is complete. 3. A method for manufacturing a tetrafluoroethylene polymer-coated roll for use in a xerographic reproducing apparatus for fixing a resin-based powder image onto paper to which the powder is loosely adhering, said method comprising the steps of:

applying to the surface of the roll a tetrafluoroethylene polymer primer in a thickness of about 0.5 mils;

heating the primer-coated roll at a temperature of from about 450 to 500 F. for 10 minutes until the primer is baked; applying to the surface of said roll a liquid coating of essentially tetrafluoroethylene enamel in a thickness of from about 0.6 to about 0.9 mil;

heating the roll to a temperature of from about to 180 F. in dry air in order to flash off water and solvent;

applying additional liquid coatings of tetrafluoroethylene enamel in a thickness of from about 0.6 to about 0.9 mil and heating the roll between successive applications to a temperature of about 170 to 180 F. until a thickness of up to about 6 mils of tetrafluoroethylene enamel on the surface of the roll is attained;

drying the coated roll in air at a temperature of between about 165 to about F; and,

heating the coated roll at a temperature of from about 730 to 750 F. for a period of from about 10 to about 20 minutes until fusion of the tetrafluoroethylene polymer coating is complete. 

2. A method for manufacturing a tetrafluoroethylene polymer coated roll for use in a xerographic reproducing apparatus for fixing a resin-based powder image onto a support surface to which the powder is loosely adhering, said method comprising the steps of: applying to the surface of the roll a tetrafluoroethylene primer in a thickness of from about 0.3 to about 0.7 mil; heating the primer-coated roll at a temperature of from about 450* to 500* F. until the primer is baked; applying to the surface of said roll a liquid coating of essentially tetrafluoroethylene enamel in a thickness of from about 0.6 to about 0.9 Mil; heating the roll to a temperature of from about 150* to 180* F. in order to flash off water and solvent; applying additional liquid coating of tetrafluoroethylene enamel in a thickness of from about 0.6 to about 0.9 mil and heating the roll after each application to a temperature of between about 150* to about 180* F., until up to about a 6 mil thickness of tetrafluoroethylene enamel is attained on the surface of the roll; and, heating the coated roll to a temperature of from about 730* to 750* F. until fusion of the tetrafluoroethylene coating is complete.
 3. A method for manufacturing a tetrafluoroethylene polymer-coated roll for use in a xerographic reproducing apparatus for fixing a resin-based powder image onto paper to which the powder is loosely adhering, said method comprising the steps of: applying to the surface of the roll a tetrafluoroethylene polymer primer in a thickness of about 0.5 mils; heating the primer-coated roll at a temperature of from about 450* to 500* F. for 10 minutes until the primer is baked; applying to the surface of said roll a liquid coating of essentially tetrafluoroethylene enamel in a thickness of from about 0.6 to about 0.9 mil; heating the roll to a temperature of from about 170* to 180* F. in dry air in order to flash off water and solvent; applying additional liquid coatings of tetrafluoroethylene enamel in a thickness of from about 0.6 to about 0.9 mil and heating the roll between successive applications to a temperature of about 170* to 180* F. until a thickness of up to about 6 mils of tetrafluoroethylene enamel on the surface of the roll is attained; drying the coated roll in air at a temperature of between about 165* to about 175* F; and, heating the coated roll at a temperature of from about 730* to 750* F. for a period of from about 10 to about 20 minutes until fusion of the tetrafluoroethylene polymer coating is complete. 